15.2. Aqueous Solutions http://www.ck12.org
aqueous solution (aq).
FIGURE 15.13
Calcium nitrate is a typical ionic com-
pound. In an aqueous solution, it disso-
ciates into calcium ions and nitrate ions.Nonelectrolytes do not dissociate when forming an aqueous solution. An equation can still be written that simply
shows the solid going into solution. For example, the process of dissolving sucrose in water can be written as
follows:
C 12 H 22 O 11 (s)→C 12 H 22 O 11 (aq)Strong and Weak Electrolytes
Some polar molecular compounds are nonelectrolytes when they are in their pure state but become electrolytes
when they are dissolved in water. Hydrogen chloride (HCl) is a gas in its pure molecular state and is a nonelectrolyte.
However, when HCl is dissolved in water, it conducts a current well because the HCl molecule ionizes into hydrogen
and chloride ions.
HCl(g)→H+(aq) + Cl−(aq)When HCl is dissolved into water, it is called hydrochloric acid. Ionic compounds and some polar compounds are
completely broken apart into ions and thus conduct a current very well. Astrong electrolyteis a solution in which
a large fraction of the dissolved solute exists as ions.
Some other polar molecular compounds become electrolytes upon being dissolved into water but do not ionize to a
very great extent. For example, nitrous acid only partially ionizes into hydrogen ions and nitrite ions when dissolved
in water. Aqueous nitrous acid is composed of only about 5% ions and 95% intact nitrous acid molecules. Aweak
electrolyteis a solution in which only a small fraction of the dissolved solute exists as ions. The equation showing
the ionization of a weak electrolyte utilizes a double arrow, indicating an equilibrium between the reactants and
products.
HNO 2 (aq)⇀↽H+(aq)+NO− 2 (aq)Lesson Summary
- A solution is a homogeneous mixture in which a solute is dissolved by a solvent. Solutions that have water as
the solvent are called aqueous solutions.